In general, compasses determine geographic orientation with reference to the Earth's magnetic field, which generally runs north and south for most populated parts of the Earth. As the magnetic poles of the Earth are not located in the same position as the Earth's geographic poles, there is an error between the geographic (true) and magnetic (compass) headings, which is called variation. Variation is location and time dependent. Conventional compasses employ a freely movable, magnetically sensitive member which aligns itself with the Earth's magnetic field and points towards the Earth's magnetic north pole.
Electronic compasses, on the other hand, determine geographic orientation without using a magnetically sensitive member. In general, electronic compasses determine geographic orientation by simultaneously measuring the magnitude of the Earth's magnetic field in at least two different directions which are related to each other at a known angle. Because the measurements are dependant upon the orientation of the measuring device, they can be used to determine the deviation of the compass's orientation from magnetic north, which gives the compass heading.
The projections of the Earth's magnetic field to the measurement plane is a function of the tilt angle of the measurement plane. Electronic compasses built around 2-axis sensors can suffer from high sensitivity to tilt errors. If the tilt angle is not kept constant during measurements there can be error. If the compass device is tilted say 10 degrees, a compass reading error of 30 degrees or more is possible.
Sensitivity to tilt differs between different geographical areas but can generally create problems for electronic compasses. High-end compasses sometimes use a tilt sensor to correct tilt errors. As this approach can be cost prohibitive, many low-end electronic compass implementations compensate for tilt error in other ways, such as through the use of a bubble level indicator. When using this type of low-end device, the user is required to keep the compass device accurately leveled during use by using the bubble indicator to manually level the compass.
While the bubble level indicator approach may provide a low cost solution if the user is in a stable environment, it is very difficult to use if the user is walking or otherwise moving. Wobbling causes tilt errors that make the compass reading noisy and difficult to read. In bad cases of wobble, the compass needle can even start spinning around. The inexperienced user judges such a device to be of very low quality.
As such, there is a need for an improved electronic compass that is capable of correcting tilt error problems in a cost effective manner.